display: Properly store later ID when adding window to queue

The code is already trying to avoid creating new laters when there
already is one for the queue type, but this wasn't working because the
ID of the later was never stored after creating a new one. This would
then result in as many laters as meta_display_queue_window() was called
and all of them would run the handler function, even if only the first
one had a non-empty window queue.

Similarly this was causing the later to not be removed if the window
queue got empty after meta_display_unqueue_window().

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2414>

src/core/display.c

@@ -4108,6 +4108,7 @@ meta_display_queue_window (MetaDisplay   *display,
           run_data = g_new0 (MetaQueueRunData, 1);
           run_data->display = display;
           run_data->queue_idx = queue_idx;
+          priv->queue_later_ids[queue_idx] =
             meta_laters_add (laters,
                              window_queue_later_when[queue_idx],
                              window_queue_run_later_func,